Model-based control of integrated diesel engine and selective catalytic reduction systems

Selective catalytic reduction (SCR) is one of the most promising solutions to meet the future nitrogen oxides (NOx) emissions regulations for heavy-duty diesel vehicles. However, during transient operations, SCR inlet temperatures can drop below the optimal range and poor NOx conversion can result. To address the low NOx conversion problems encountered particularly in low load conditions, a new integrated engine and aftertreatment control strategy was investigated. This integrated approach improves the SCR system efficiency by using available feedback and modulating the upstream air/fuel ratio to provide more favorable SCR inlet conditions. In order to integrate the engine and aftertreatment system, a model of the SCR dynamics was created and validated and a simple model of the relationship between the engine's air/fuel ratio and resulting exhaust temperature and composition was leveraged. The new model-based control strategy is proven to be effective in improving the NOx conversion efficiency of the SCR system from 35% to 85% at low load operating conditions.

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